In recent years, for internal combustion engines, in order to achieve low fuel consumption of the engines, there has been a trend toward reduction in tension of a combination oil ring for the purpose of reducing friction. However, as tension of an expander spacer is set lower, two segments (side rails) arranged respectively on an upper side and a lower side apt to perform individual rotation in a circumferential direction. In such rotational motion, when gaps of the upper and lower segments are aligned in an up-and-down direction, oil that remains unscraped is conveyed to an engine combustion chamber due to the presence of the gaps. As a result, there arises a problem in that excessive supply of oil causes increase in oil consumption.
In order to solve such problem, it is required that individual rotation of the segments be prevented. For prevention of such individual rotation, for example, in Patent Literature 1, there is disclosed a configuration in which an inner peripheral surface of a segment in contact with an expander spacer has fine projections and recesses. Moreover, in Patent Literature 2, there is disclosed a configuration in which an inner peripheral surface of a segment has slit portions. Pitches of the slit portions are equal to pitches of ears of an expander spacer, and are equal in interval to a width dimension of the ears.
Moreover, in Patent Literature 3, there is disclosed a configuration in which inclined fine projections and recesses are formed along a contour of an ear in an inner peripheral surface of the segment held in contact with an expander spacer. Moreover, in Patent Literature 4, there is disclosed a configuration in which a plurality of grooves are formed in an inner peripheral surface of a segment by radiating laser to an inner peripheral surface of a wire member of a segment formed into an annular shape. Moreover, in Patent Literature 5, the following configuration is disclosed. That is, a soft metal plating layer is formed on an inner peripheral surface of a side rail. The soft metal plating layer has a micro-Vickers hardness of from 150 to 350 and a film thickness of from 5 μm to 30 μm. Further, a nitriding layer is formed on a surface of an expander spacer.